How to sex a pterosaur

A recent paper reports the exciting news that a new pterosaur fossil has been found in China (by a farmer), there’s been quite a bit of media coverage of this find over the last few days, but why the excitement? And what actually is a pterosaur? And why would you want to sex one?

Pterosaurs’ were ancient reptiles that could fly, they had modified front-legs that acted as wings and they lived at the same time as the dinosaurs (around 220 to 65 millions years ago). Although they weren’t actually dinosaurs, they were another kind of reptile, like the dinosaurs they were wiped out in the same mass extinction event 65 million years ago. Sometimes they’re called pterodactyls, which I admit, is a cooler name.

The name Pterosaur actually refers to a whole order of different species, like the word lizard refers to a whole range of different forms. The recent find was of a species from the Darwinopterus genus, guess who it’s named after?

This pterosaur was pregnant with an egg when it died, and the fossil evidence suggests it had broken its arm, so it may have become injured when flying (maybe it was hurt in a storm, hit by volcanic debris, attacked by another pterosaur, who knows?), and then likely fell into a lake, sunk and was buried in the sediment, where it was fossilized. What makes this fossil really interesting is the egg. Palaeontologists can tell a lot about pterosaurs from this egg. These are the two most exciting implications:

1. Previously most experts believed pterosaurs laid eggs in a fashion more similar to birds than reptiles. Birds lay a small number of large eggs and tend to care for them. They invest quite a lot of energy into each of their offspring. Whereas reptiles tend to have a lower-investment strategy, laying greater numbers of smaller eggs, and usually not caring for their eggs or offspring. The pterosaur egg looks much more similar to a reptile than a bird egg, so the palaeontologists who found the fossil are confident that pterosaurs had a low offspring investment strategy like reptiles, likely burying their eggs and leaving them rather than incubating them by sitting on them.

2. The second cool implication is that palaeontologists now know for sure that pterosaur fossils that look like this one are female. Two different forms of pterosaur fossil had been found for this type; one had an ornate head crest and a small pelvis, the other had no head crest and a large pelvis, just like the recent fossil. Experts have concluded that males and female pterosaurs of this species therefore looked different (this is called sexual dimorphism), females were the ones without the head crest, males were the ones with them.

Sexual dimorphism is common in many types of animals, particularly birds and reptiles, and commonly it’s the males who have bright colours and features like crests. Think of peacocks, the females are generally brown and not particularly exciting, whereas the males have huge tails with iridescent blue and green feathers. This is usually because the males have to compete with each other to mate. Females may only choose to mate with only one or a small number of males, so males are under huge competitive pressure if they want to pass on their DNA to the next generation. Sometimes males compete by fighting, but often they show how healthy and successful they are by developing extravagant features. Often these features make them more vulnerable to attach by predators, male peacocks aren’t exactly well camouflaged! Males thus have to balance the risk of being eaten, with looking awesome, and getting laid.

And it looks as though this may have been the same with pterosaurs, or at least this species. This is an interesting finding in itself, but its also useful for palaeontologists to understand which of their fossil pterosaurs are male or female, as this allows them to look for further differences between males and females, like size, and allows them to look for the same pattern of sexual dimorphism in other pterosaur species. This may help to understand whether different looking fossils are part of the same species or are different species, which will improve the overall understanding of pterosaur species and the evolutionary relationships between them. Which is good. It’ll make pterosaurs an easier group of animals for palaeontologists to understand.

There, press excitement explained.

By the way, the coolest pterosaur is Quetzalcoatlus, because it was huge, with a wingspan of 11 meters! OK, that’s not got much to do with this story, but don’t act like you aren’t impressed.

I’ve not seen any Creationist reactions to this yet, but it’s sure to come, as they hate pterosaur fossils!

Hi Bob, sorry it took me so long to reply, I’m in the middle of Uni exams at the moment.

I’m no expert so I don’t have any idea how many fossils have been mistakenly identified, but I agree its a great find, and I love that science adapts to new information so that a new piece of evidence can change how we see the world

Thanks for the reply Dan. Some times in our careers we have to go for the money. Science is always there. I was a high school science teacher. I loved science but it wasn’t the driving factor in education. Science can be applied to any problem and I have moved on into astronomy and paleontology.